I’ve been advocating adding tracers to fracking fluids, and not just for research. Tracers can allow following water movement from individual wells, for example, so that liability can be assigned in the event of ground or surface water contamination, even decades after a well is closed.

EPA’s science advisory board is on the right track, where they say in their scoping document that

The potential and desirability of introducing tracer constituents in hydraulic  fracturing fluids for studying fate and transport in these complex fractured systems should also be investigated.